Conformational Ensembles from Experimental Data and Computer Simulations

Conformational Ensembles from Experimental Data and Computer Simulations

Poster Abstracts

82-POS Board 2 In Silico Study on the Activation Mechanism of Chemokine Receptor CXCR4 in Complex

with Chemokine CXCL12 and Gα i Protein Kingsley Theras Primus Dass , Hao-Jen Hsu. Tzu Chi University, Hualien, Taiwan.

The chemokine receptor CXCR4 belonging to rhodopsin superfamily of GPCR is commonly expressed in immune cells and central nervous system. Engagement of CXCR4 in regulating the cell migration and developmental process make CXCR4 an important drug target. Higher expression of CXCR4 on the cancer cells recruits CXCL12 leading to the metastatic condition. So far, many studies have reported the interaction between CXCR4 and CXCL12 but failed to explain the detailed signal transduction of CXCL12 to CXCR4. In this study, we investigated the binding and activation mechanism of CXCR4 in complex with CXCL12 and Gαi by docking and molecular simulations. CXCL12 was docked to the full-length CXCR4 with homology modeled N-terminus. Two preferable poses, Pose-36 and Pose-597, were selected for further multi- microsecond MD stimulations. MM/PBSA binding free energy calculations revealed Pose597 has lower binding free energy than Pose-36. For the complex of Pose-597, the simulation showed that the TM1, TM6, TM5 and ECL 3 underwent large fluctuations and a kink formation in TM7 was observed. Moreover, to explore the complete activation mechanism of CXCR4, Gαi with GDP bound was docked to the CXCR4 complex after 1.5 us MD simulations. The MD stimulation of the ternary complex showed that the N-terminus of Gαi fluctuated to cause its helix α5 approaching the cytoplasmic pocket of CXCR4, increasing the distance between the two domains of Gαi, which leads to the release of GDP. CXCR4 with the mutated L244 6.40 N was developed to examine the activation without its ligand CXCL12 binding, which showed that the N-terminus of mutant CXCR4 flipped out for signal transmission. These results give a detailed understanding about the signal transmission through Gαi, which would be helpful in the development of anticancer drugs.

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